1. Field of the Invention
The present invention generally relates to magnetic recording media used in magnetic recording and reproducing apparatuses, and, more particularly, to a substrate for a magnetic recording medium that can reduce the floating height of the magnetic head in compliance with higher recording densities. The present invention also relates to a method of evaluating a magnetic recording medium that can reduce the floating height of the magnetic head.
2. Description of the Related Art
For a magnetic recording medium, such as a magnetic disk, the substrate is produced by providing nickel-phosphorus plating on the surface of an aluminum alloy, for instance, and polishing the resultant. On the surface of the substrate, irregularities are formed by a texture process. The reason why those irregularities are positively formed on the surface of a magnetic recording medium is that the magnetic head can magnetically record and reproduce information on the magnetic recording medium while maintaining a very small floating height from the magnetic recording medium. In this manner, the magnetic head can be prevented from adhering to the surface of the magnetic recording medium, and the frictional resistance can be reduced.
In recent years, however, there has been an increasing demand for higher-density magnetic recording and reproduction apparatuses, such as magnetic disk devices used in computers. In response to such a demand, it is necessary to reduce the magnetic spacing between the magnetic head and the magnetic disk, i.e., the floating height of the magnetic head, as much as possible. Recently, a glide height value that is the distance from the disk average surface is required to be 10 nm or less, and a head floating height is required to be 30 nm or less.
Japanese Laid-Open Patent Application No. 9-326115 discloses a technique of reducing the head floating height by evaluating the undulations and ripples formed by the irregularities on the surface of a magnetic recording medium.
Also, a magnetic recording medium having a non-texture process performed thereon has been suggested. The non-texture process is performed to restrict the irregularities on the surface within a predetermined range so as to reduce the head floating height. However, the non-texture process cannot solve the problem of head adhesion.
The technique disclosed in Japanese Laid-Open Patent Application No. 9-326115 involves the evaluation of the undulations and ripples in the circumferential direction (the recording and reproducing direction of the magnetic head). In this technique, the floating height of the magnetic head is restricted to 100 nm or smaller. In recent years, however, there has been a demand for magnetic heads having even smaller floating heights, such as 30 nm or less. As a result, it has become difficult to realize such a small floating height only by putting a restriction on the shapes of irregularities in the circumferential direction of the magnetic disk.
Furthermore, in the conventional magnetic disk apparatuses, a contact start stop (CSS) method in which the floating surface of the magnetic head is brought into contact with the surface of a magnetic disk and then slidably moves on the surface of the magnetic disk is widely employed. In order to reduce the floating height, it is necessary to perform the texture process and reduce the heights of the irregularities on the surface of the magnetic disk. However, if the irregularities on the surface of the magnetic disk are made too small in height, the surface of the magnetic disk is smoothed. This will result in the problems of the adhesion and high friction of the magnetic head at the time of contact start and stop.
A general object of the present invention is to provide substrates for magnetic recording media in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a substrate for a magnetic recording medium that is formed by a predetermined material so as to reduce the floating height of a magnetic head.
Another specific object of the present invention is to provide a method of evaluating a magnetic recording medium that can reduce the floating height of a magnetic head.
The above objects of the present invention are achieved by a substrate for a magnetic recording medium that comprises a sintered body provided with pores having a diameter in the range of 0.05 xcexcm to 2.0 xcexcm extending across 5% to 50% of the surface area of the substrate.
With this substrate for a magnetic recording medium, the surface of the substrate is provided with a large number of pores even if the surface appears to be flat. Accordingly, a magnetic recording medium formed by this substrate has only a small contact area with the magnetic head. Even if the floating height becomes small and the magnetic head is brought into contact with the surface of the magnetic recording medium, there will be no problem of adhesion and high friction with the magnetic head.
The above objects of the present invention are also achieved by a method of manufacturing a substrate for a magnetic recording medium, comprising the step of sintering a particle material containing a porous material at a temperature higher than the melting point of the porous material. The particle material may be aluminum particles. The porous material is not specifically limited, but should preferably be one material selected from the group consisting of lead, copper, magnesium, nickel, zinc, tin, manganese, silicon, glass, and resin.
By this method, when a magnetic layer and a protection layer are formed on the substrate, the floating height of the magnetic head can be reduced, thereby obtaining a magnetic recording medium having a higher recording density.
The above objects of the present invention are also achieved by a method of evaluating a magnetic recording medium, comprising the steps of:
measuring the maximum height of each of a plurality of waveforms having different wavelengths in the moving direction of a magnetic head on the surface of the magnetic recording medium; and
determining the sum of the maximum heights of the plurality of waveforms.
This method further includes the steps of:
measuring the maximum height Wp of undulations having a wavelength of 2.5 mm or larger in the recording/reproducing direction of the magnetic head, the maximum height MWp of ripples having a wavelength in the range of 10 xcexcm to 2.5 mm, and the maximum height Rp of minute ripples having a wavelength of 10 xcexcm or smaller; and
comparing a required glide height value with the sum of Wp, MWp, and Rp,
wherein the maximum height RCmax of irregularities in the scanning direction of the magnetic head is 20 nm or smaller in the floating guaranteed area (or the recording area) on the magnetic head.
By the above evaluation method, the glide height value required for a magnetic recording device is determined and then compared with the sum of Wp, MWp, and Rp. In this manner, it is determined whether or not the magnetic recording medium is suitable for high-density recording with a small floating height.
It should be understood here that the moving direction of the magnetic head is the radial direction of a disk while the recording/reproduction direction of the magnetic head is the circumferential direction of the disk. The moving direction and the recording/reproduction direction of the magnetic head are perpendicular to each other.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.